THE GREEN-HOUSE. 



15 



Fig. 6. 



But this elegant plan, and all others where the 

 surface is composed of curved lines, is more expen- 

 sive to execute than where straight lines only are 

 employed; and therefore the question of greatest 

 practical importance is, what form of straight-lined 

 surface will answer best as to the admission of the 

 sun's rays ? The answer is obvious — a polygon, or 

 many-sided figure, founded on a semi-dome. 



All other circumstances being suitable, the cur- 

 vilinear form (fig. 6.), and polygonal form (fig. 7.), 

 are the best for either a green-house or a conservatory; 

 but these forms will not always harmonize with other 

 circumstances, and therefore must frequently give 

 way to such as are more economical or better adapted 

 to particular situations. 



